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CLOSE THIS BOOKTools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)
Technical Chapter 7: Stoping
VIEW THE DOCUMENT7.1 Pneumatic jack hammer, drilling stand, jackleg
VIEW THE DOCUMENT7.2 Gasoline hammer drill
VIEW THE DOCUMENT7.3 Wedge ram
VIEW THE DOCUMENT7.4 Electric hammer drill with stand Y D Z
VIEW THE DOCUMENT7.5 Manual mining methods
VIEW THE DOCUMENT7.6 Pneumatic charging machine for explosives

Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)

Technical Chapter 7: Stoping

7.1 Pneumatic jack hammer, drilling stand, jackleg

Stable Rock Deep Mining, Stable Rock Open-Pit
Underground Mining, Extraction Mining

germ.:

Pneumatischer Bohrhammer, Bohrstutze, Teleskopstutze

span.:

perforadora neumatica, pie de apoyo, apoyo telescopico

Producer:

Atlas Copco, Montabert, SIG, Bohler, Tamrock, Mannesmann Demag, Barrenos: Barrenos Sandvik SA, ADESUR, Fagersta Secoroc de Peru

DATOS TECNICOS:


middle weight lack-h

light weight lack-h

drilling stands

Weight:

22 - 29 kg

9.5 kg

13.5 kg

Length:

60 - 70 cm

approx:50 cm

800 - 1.650 mm

Piston :

58 - 90 mm

66 - 75 mm


Stroke length:

45 - 70 mm

750 - 2.000 mm


Single strike energy:

48 - 150 Nm



Number of strokes:

2.200 - 3.400 min-1

3.500 min-1


Strike capacity:

1.9 - 5.5 Kw



R.P.M.:

160 - 240 min-1

280 min-1


Rotation angle:

20° - 30°



Torque:

100 - 150 Nm



Compressed air consumtion:

2.4 - 5.6 m3/min


1.4 m3/min

Drill hole :

27/41 - 34/5 mm



Max. Iength of drill hole:

4 - 6.5 m



Working pressure:

3 - 7 bar

3 - 7 bar


Opt. working pressure:

5 - 6 bar

5.5 bar

5 - 6 bar

Rate of drilling progress:

up to 35 - 100 cm/min



Drilling equipment:

monobloc drilling rods with male end hexagonal 22 mm (7/8 inch) × 108 mm working length of:


800 mm with 34 mm diameter and 3.0 kg weight


1600 mm with 33 mm diameter and 5.4 kg weight


2400 mm with 32 mm diameter and 7.9 kg weight


as well as lengths in-between according to the supplier

Operating Materials:




Which:

oil

water

Pwater= Pair-1 (bar)

Quantity:

small amount as lubricant

drilling water 3/4" supply


ECONOMICAL DATE:

Investment Cost:

2500 DM - 6000 DM jack-hammer; approx. 4000 DM/piece (used) incl. stand; drilling stand approx. 2000 - 3000 DM/piece

Consequential Cost through Coupling Effects:

cost of compressed air supply

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————|high

Maintenance Experience:

low |————|————|high

Personnel Requirements:

low for handling

Adjoining Rock Requirements:

Almost without exemption, all adjoining rock can be drilled in; in cases of very soft adjoining rock, rotating or rotating-percussion drilling is applied to that drill cuttings or debris can be removed easily.

Regional Distribution:

worldwide

Experience of Operators:

very good |————|————|bad

Environmental Impacts:

low |————|————|very high


Especially in cases of insufficient water or air circulation, dangerous dust pollution occurs: Silicosis

Suitability for Local Production:

very good |————|————|bad

Lifespan:

very long |————|————|very short

Bibliography. Source: AC-Handbook, Stout, Fritzsche, Reuther, Roschlau

WORKING PRINCIPLE:

The pneumatic Jack-hammer works with a centrifugal piston driven by compressed air with strokes ranging between 1,800 and 3,500 min-1 in reciprocating motion and is controlled by a flutter valve. After a forward motion, when the admission strike reaches the bigger cylindrical chamber, the centrifugal piston hits the male end of the drilling rod. As the strike reverses, the male end is rotated by spinning grooves at the centrifugal piston. The rotation device with a pawl and ratchet mechanism allows rotation only in one direction. Thus, the cutting edge of drilling steel always hits another sector of the bottom hole. A central water supply leads through the centrifugal piston and male end to the flush. The flushing fluid then cools the drilling steel, removes drill cuttings or debris, and binds possible silicone dusts.

Drilling stands guide the percussion bit into the hole and transmit the thrust to the hammer. Such drilling stands composed of pneumatic telescoping cylinders, are fed with compressed air and fixed in an inclined position at the bottom hole. Depending upon the design, air pressure and therefore the thrust can be controlled either directly at the hammer or at the stand. A pneumatic device withdraws the hammer.

In drilling rise heading and vertical holes in upward designed mining, such as in steep vein ore deposits, the so called stop-hammers are used which are fixed at the stand.

Repeated sharpening of drilling bits or steel is very important for the drilling progress as well as for a long-lasting drilling equipment. This can be done by small compressed air driven grinding machines fixed on a tripod and equipped with a vice to fix the drilling bits. The most important standards for carbide bits, e.g., wedge angle, cutting edge curve, coefficient of wear and lateral angle are controlled by pattern. The standing time of drilling bits until they have to be sharpened are in correlation to the wearing hardness of drilled rock. The following table shows after what rate of penetration sharpening becomes necessary

Kind of rock

Drilling meterage

Sandstone

8 - 16

Sandy shale

20 - 30

Shalestone

50 - 100

Gneiss, granite

3 - 6

Older rock salt

30 - 36

Carnalitite

40 - 50

Hard salt

22 - 100

REMARKS:

Percussion and rotating-percussion hammers need high thrust.

It should be taken in mind to avail of small jack hammers with stand such as the Tll of Montabert weighing 9.5 kg and consuming 1.4 m³/min compressed air. The low capacity could be amended by higher explosives. Additional cost for this should be taken In relation to the lower cost of compressed air supply.

Instead of supplying water in a costly pipe system, water can be carried by mobile tanks, in which the resuming space is filled with compressed air.

Cost of percussion drilling:

Jack hammer

approx. 50 %


Compressed air

approx. 10 %


Percussion drill bit

approx. 40 %

In pneumatic drilling, the degree of efficiency with the corresponding applied energy is very low considering the losses in the production of compressed air and lies between 1 to 10%, depending upon the parameters used. Aside from losses during the production and distribution of compressed air, losses also occur during transmission of power in percussion, sound insulation, friction at the drilling hole wall as well as during reflexion of percussion energy into the drilling rod.

A further source of losses is in the connection of drilling rod, bit, and possibly of extension rods. Power loss of each connection is approx. 5 %. To avoid such losses, using monobloc drilling machines and avoiding extension rods can be done.

Since jack-hammers are usually delivered with a left turning rotation, they should be ordered with a right turning rotation for anchor setting, so that the anchor nut can be tightened with the hammer which is equipped with a special device.

The thrust which needs a medium-sized hand hammer, ranges between about 60 to 120 kg. Of this, only an average of approx. 5 kg can be done by the hammer manually or without any mechanical aid. Heavier dead weights lower the backward thrust of hand-held percussion drilling machines.

In order to be able to distribute the needed high thrust, an optimal angle of attack of the stand has to be selected. It should be always smaller then 40.

After a distance of 5 - 10 cm and starting with a low thrust, more power can then be applied.

Instead of a pneumatic drilling stand, the mexican method and a system comprising of two ladders and one slide board can be used for light weight hammers.

Before assembly of the drilling system begins, hoses have to be blown out in order to avoid water hammer destroying the drilling machine.

Pneumatic mining hammers are used for minerals that don't require drilling and blasting due to their low degree of hardness. Only a forward and backward motion is transmitted by the centrifugal piston to the striking bit. Rotation and flushing of water are excluded.

SUITABILITY FOR SMALL-SCALE MINING:

Pneumatic jack hammers are suitable for all drilling purposes in underground and open-pit mining due to their low weight and high stability, however, they need expensive power supply.


Fig.: Jack-Hammer with water jet, 1) jet, 2) feed line for compressed air, 3) feed line for water supply. Source: Roschlau.

Multiplers to detrmine the air consumption of rock and drills at various altitudes


Number of drills

Altitude

1

2

3

4

5

6


Multipliers

ft.







0

1.0

0.9

0.9

0.85

0.82

0.8

1.000

1.0

0.95

0.93

0.87

0.84

0.83

2.000

1.1

0.97

0.95

0.92

0.88

0.86

3.000

1.1

1.0

1.0

0.95

0.92

0.9

4.000

1.1

1.05

1.03

0.97

0.94

0.93

5.000

1.2

1.1

1.07

1.02

0.98

0.96


Fig.: A drilling stand. Source: Fritzsche


Fig.: Quality control of drilling bit sharpening, a) wearing control, b) control of wedge angle, c) control of open angle curve. Source: Roschlau.


Fig.: Cross-section of a jack-hammer. Source: Reuther.

1.

compressed air adapter

10.

behind cylinder room

18.

canal

2.

free room inside the cylinder head

11.

cover

19.

cylinder

3.

valve chatter

12.

cover room

20.

piston shaft

4,5.

canal

13.

canal

21.

twist nut

6.

front cylinder room

14.

exhaust arris

22.

leader nut

7.

percussion piston

15.

front piston arris

23.

drill sleeve

8.

behind piston arris

16.

arris at the piston shaft

24.

shank

9.

exhaust arris

17.

wearing box

25.

drill sleeve





26.

ratchet wheel


Fig.: Design of a jack-hammer with stand, a) for thrust, b) stop-hammer. Source: Armstrong.


Fig.: Composition of a complete drilling system for pneumatic drilling with stand. Source: Atlas Copco Company Information.

1. jack-hammer
2. coupling
3. stand
4. extension for stand
5. flush water hoses with claw coupling
6. compressed air hoses with claw coupling
7. oil lubricator
8. water separator


Fig.: Drilling bits for percussion drilling, 1) hard metal tip 2) flush hole 3) bit neck 4) hard metal pins. Source: Roschlau

7.2 Gasoline hammer drill

Stable Rock Deep Mining Stable Rock Open-Pit
Underground Mining Drilling Mining

germ.:

Benzingetriebener Bohrhammer, "Cobra", "Pionjar", Brennkrafthammer

span.:

motoperforadora, camera de combustion

Producer:

Atlas Copco

TECHNICAL DATA:

Dimensions:

75 × 50 × 35 cm HWL



Weight:

25 or 23 kg /26 kg



Extent of Mechanization:

fully mechanized



Form of Driving Energy:

eternal combustion engine 185 cm3/2500-2700 R.P.M.

Mode of Operation:

semi-continuous

Throughput/Capacity:

250 - 300 mm/min thrust in granite

Operating Materials:


90/100 Pionjar:


Which:

gasoline

80/100 octane, also lead free

oil/SAE 40

Quantity:

approx. 1.5 I/h

1: 12 (8 %) pionjar

1: 20 (5 %)

ECONOMICAL DATA:

Investment Cost:

approx. 5000 DM



Operating Cost:

high cost of fuel



Consequential Cost through Coupling Effects:

special sucking ventilation for underground operations is necessary

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Experience:

low |————————| high

Mining Requirements:

Gasoline driven jack-hammer can only drill in horizontal or downward approach, but in exceptional cases, up to 45° upward. The reasons for that is the direct coupling of engine and carburetor. Advantages are mining methods which lead downward and so allow bench drilling.

Replaceable Equipment

compressed air hammer drill

Availability of Technique:

import is necessary

Regional Distribution:

so far unknown in small-scale mining in Latin America

Experience of Operators:

very good |————|————| bad

Environmental Impacts:

low |————|————| very high


contamination of the environment with exhaust and used oil

Suitability for Local Production:

very good |————|————| bad

Lifespan:

very long |————————| very short

Bibliography, Source: AC-Handbook

OPERATING PRINCIPLE:

Gasoline hammer drills operate with a twin-piston internal combustion engine. One part of the piston is a centrifugal piston which functions as a striking piston, whereas the other part is used for the transmission of drilling rods and compression air in order to blow clean the drilling hole.

AREAS OF APPLICATION:

Drilling of downward and possibly horizontally aligned blasting holes of underground and open-pit mining with hard or solid rock.

REMARKS:

Grinding machines with bending shaft and centrifugal pump are available as auxiliary equipment to drive gasoline fed hammer drills.

Very problematic are the following:

- somewhat heavy weight is specially when working at or near a hanging wall

- exhaust with high CO content. Special ventilation is absolutely necessary. Long hose for exhaust lowers efficiency

- reduced efficiency of up to 50 % in high altitudes of Latin American small-scale mines

- pulling of drill rods without extra equipment is often difficult or impossible

- drilling is dry resulting to enormous dust development.

General internal combustion engines are dangerous in underground mines and need special ventilation due to high CO-content in the exhaust. The use of such machines is not advisable especially in small-scale underground mining which often lack sufficient ventilation. The advantage of being independent from an underground power supply system is being neutralized by the expenses for a special sucking ventilation.

There is a high danger of silicosis development when working in hard or solid rock where quartz stones are drilled.

Pionjar is more suitable for high altitudes in developing countries than the Cobra. On one hand, the needle carburetor can be adjusted to a higher altitude, on the other hand, its design is simpler than the diaphragm carburetor of the Cobra

Already used in Afghanistan in blasting short tunnels for storage rooms. There they were used with slides on stands.

Analogous to pneumatic mining hammer, gasoline driven mining hammers are available for easily exploitable minerals such as coal.

SUITABILITY FOR SMALL-SCALE MINING:

Not suitable for application in running underground operations due to environmental and safety problems. Application or use seems right only for special works without compressed air infrastructure and in open-pit mining for hard sediments.


Fig.: Cross-sectional sketch of a Cobra gasoline hammer. Source: Atlas Copco company Information

7.3 Wedge ram

Stable Rock Deep Mining Stable Rock Open-Pit
Underground Mining Extraction Mining

germ.:

Rammkeil, Gesteinsbrecher nach Francois

span.:

rompedor de rocas, segun Fran,cois

TECHNICAL DATA:

Dimensions:

length about 4 m

Weight:

approx. 30 kg + 45 kg driving ram

Extent of Mechanization:

not mechanized

Form of Driving Energy:

manual

Mode of Operation:

intermittent

Operating Materials:

none

ECONOMICAL DATA:

Investment Cost:

self-made: 250 - 500 DM

Operating Cost:

exclusively labor cost

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Experience:

low |————|————| high

Mining Requirements:

no breakings can be cut by wedge ramming, which means full work is not possible with wedge ram

Replaceable Equipment:

blasting explosives

Regional Distribution:

mostly replaced by blasting explosives, application where ram or blast effects have to be controlled, e.g., in natural stone mining, marble quarries etc.

Environmental Impacts:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under what Conditions:

good metal manufacture with good welding technique and can operate with tenacious steel

Lifespan:

very long |————|————| very short

Bibliography, Source: Lengemann

OPERATING PRINCIPLE:

Four springs are inserted Into the drilling hole. The wedge which leads to a quadratic area for the ram is then being rammed into the remaining space. The four roles being integrated into the ram lower the friction. The ram is pulled with a pulling rope over a pulley against the inset.

AREAS OF APPLICATION:

Extraction of coarse debris in hand tramming works in the mine heading. Application in mining of natural stones.

REMARKS:

Due to insufficient crushing, problems in transporting coarse debris occur. The use or application of wedge ram is right in friable bedrock or in open-pit mining where possibly large blocs have to be extracted ( e.g. marble).

Cut or sawed marble yield higher prices than blasted marble for sculpting purposes. The latter contains fine micro splits which can lead to a sudden breakage of other parts during treatment.

SUITABILITY FOR SMALL-SCALE MINING:

For underground ore mining, this technique has only a limited application but it is quite suitable for open-pit mining.


Fig.: Design and work principle of a wedge ram. Source: Lengemann Fig. 4: Wedge ram by A and J. Francois. The 4 springs a, a', a, a', are being inserted into the drill hole and if necessary the spring e in-between a and a'. In the remaining space o (compare fig. 4b) the wedge b is rammed In that has backward a quadratic guide f for the quadratic hole of 45 mm width of ram R. The 4 roles r that are let in the latter are minimizing friction. The shackle 9 serves to fix pulling rope Z through pulley v (compare fig. 4b). The ram can also being moved by a tin iron rod with handle, which is fixed at shackle g. K locking pin to limit the ram lifting.

7.4 Electric hammer drill with stand Y D Z

Stable Rock Deep Mining, Stable Rock Open-Pit
Underground Mining Extraction Mining

germ.:

Elektrischer Bohrhammer auf Stutze

span.:

perforadora electrica sobre apoyo

Producer:

China Mining Technology Consultant Centre

TECHNICAL DATA:

Dimensions:

610 × 335 × 220 mm + stand

Weight:

30 kg + drilling rod, supply cord, water hose

Extent of Mechanization:

fully mechanized

Driving Output

2 kw

Form of Driving Energy:

electric: 3 phases, 127 V, 15,7 A, 50 Hz

Mode of Operation:

semi-continuous

Throughput/Capacity:

> 3 kg × m hammer impulse, > 150 kg × cm rotation impulse, 2640 min-1, holes up to 4 m 34 - 43 mm, drilling rods 22 or 25 mm, hexagonal with central flush

Technical Efficiency:

65 %

ECONOMICAL DATA:

Consequential Cost through Coupling Effects: power supply

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|———| high

Maintenance Experience:

low |————|————|high

Location Requirements:

none, machine is explosion proofed

Mining Requirements:

power supply needed up to the mine heading

Repleaceable Equipment

pneumatic hammer drills

Regional Distribution:

China

Environmental Impacts:

low |————|————| very high

low oil consumption in comparison with compressed air

Suitability for


Local Production:

very good |————|————| bad

Lifespan:

very long |————————| very short

Bibliography, Source: Company information

OPERATING PRINCIPLE:

With 3-phases-alternating current driven percussion hammer drill with stand and external water coolant and flush.

AREAS OF APPLICATION:

Drilling in heading and winning of mechanized small-scale mines with power supply for all rock types.

REMARKS:

Efficiency of electrical systems is significantly higher than that of pneumatic systems, which means, it requires less input for primary energy.

The performance of electrical systems is dependent of external air, which means efficient operation can be done also in greater heights.

The environmental impact (oil suspension, noise pollution, etc.) of electric hammer drills is comparably low or not existing at all.

In the case of lifespan and maintenance, doubts still remain as there has been no experience on these yet. Particularly for drilling equipment, small-scale mining maintains high standards for stability and lifespan. So far, pneumatic systems rank first under these aspects.

Besides electric hammer drills, electric mining hammers ( without rotation and flush) for cutting bits are also being marketed. They are used mainly in coal mining.

Electric Systems are only advisable if transmission from a public power supply net is available. Disadvantages of an electric mechanization in underground mining are the results of:

- sensitive technique especially of the percussion device of hammer drills
- safety problems
- low marketability.

SUITABILITY FOR SMALL-SCALE MINING:

The electric hammer should be considered as an alternative to pneumatic systems in small mines with only few working places. Its low Input of primary energy needed and environmental soundness are marks of the electric hammer, however, high cost of installation of electric power supply should be considered in the case that it is not available.

7.5 Manual mining methods

Deep Mining in Soft Rock
Underground Mining Extraction

germ.:

Manuelle Gewinnungstechniken

span.:

tecnicas de explotacion manual

TECHNICAL DATA:


Extent of Mechanization:

not mechanized

Form of Driving Energy:

manual

Mode of Operation:

intermittent

Throughput/Capacity:

capacity is very low compared with winning capacity of fully mechanized working units

Operating Materials:

none

ECONOMICAL DATA:


Investment Cost:

low

Operating Cost:

predominantly labor cost, additionally cost of wearing parts (drill bits, drill steels)

Consequential Cost through Coupling Effects:

none

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Experience:

low |————|————| high

Ore Requirements:

soft rock

Adjoining Rock Requirements:

most favorable deposits are those with stable adjoining rock and comparably soft or loose material to be mined, e.g., that of some oxidation zones, coal seams, etc.

Replaceable Equipment:

mechanized mining

Regional Distribution:

worldwide

Experience of Operators:

very good |————|————| bad


extremely high physical stress, wherever exploitation of hard raw materials is required

Environmental Impacts:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under what Conditions:

hammers, picks, chisels bits, eventually drill rods can be produced bylocal small scale industry, and probably simple hand drilling machines, in metal manufactures

Bibliography, Source: Fritzeche, Roschlau

OPERATING PRINCIPLE:

Manual mining techniques are mostly applied in soft rock in underground and open-pit mining. To be distinguished are the following:

1. Manual working with pick and shovel. Predominantly in coal mining but also in extraction of ore from residual zones and consolidated loose material, such as in gold mining wherein extracted ore is cut with a pick.

The miner often uses the method of "undermining" by drifting a split into the wall face near the bottom and cutting upward by making use of gravity.

First and foremost, this technique is common in an artisan coal mining.

2. Manual drilling by rotation and blasting. In small-scale mining more solid materials can be cut with manual rotating drills (such as Lisbeths hand rotary drill) and by blasting. These include such materials as coal, salt, sulfa, shale, gypsum, etc The drilling machines are hand driven, have a manual thrust, are guided by a stand braced at the drilling hole and operate with a percussion drill but without a flush. An auger bit removes the drill cut of the hole. The objective of any drilling is to adjust the thrust so that the chips are cut off with the maximum size in order to guaranty the lowest possible work effort for cutting. The lifespan of hand drill drilling rod is very high and lies within a minimum of 3,000 m. Attached to the drilling rods are exchangeable symmetrical or asymmetrical slot-and-cut bits with hard facing. The time duration between each sharpening is equivalent to 30 - 150 meterage, the total lifespan after about 15 - 25 sharpenings is approx. 2,000 meterage. The stands for hand driven drills are comprised of a telescoping double-tube frame which is braced with an adjusting screw at the fixing point and to the hanging wall.

3. Hard rock materials can be broken by manual percussion drilling of blasting holes and by blasting. This is a technique which is widely applied up to now in small-scale mining for high quality ore, such as gold ore, tungsten, tin and precious stones. The advancing distance per round here is shorter than in mechanized mining and is on the average of about 30 cm. A main problem is the discharging of drill cuttings or debris from the drilling holes. Most suitable therefore are small scrapers with flattened bended end. They are placed into the drill hole to scrap out drill cuttings.

Here, productivity is seen as the volume of cuttings per shift and is about 3 - 5 times as high as that of the hammer and chisel or manual minining without blasting.

AREAS OF APPLICATION:

Manual winning or extraction of raw materials in underground and open-pit mining, mainly for soft and medium soft rock.

SUITABILITY FOR SMALL-SCALE MINING:

Manual extraction In small-scale mines of the developing countries is important where no mechanization of underground work is being planned.


Fig.: Mining tools. Source: Trptow.


Fig.: A Lisbeth hand drill. Source: Treptow.


Fig.: Mining tools. Source: Lengemann

Fig. 1 - 5 double-pointed picks, fig. 1 - 3 with removable blades and fig. 1 - 2 retaining flanch on helmet by using fig. 3 a wedge following the Acmes method. Fig. 6 and 7 simple pick. Fig. 8 simple pick with removable blade. Fig. 9 and 10 pick with detachable bits. Fig. 11 cutting pick. Fig. 12 double-pointed cutting pick. Fig. 13 - 15 Belgium cutting pick. Fig. 16 acute hammer.

7.6 Pneumatic charging machine for explosives

Deep Mining General Open-Pit Mining General
Underground Mining Extraction

germ.:

Pneumatische Sprengstoffpumpe, Injektorpumpe

span.:

bomba neumatica pare explosivos, bomba inyectora

TECHNICAL DATA:

Dimensions:

70 × 70 × 100 cm LWH including tank for blasting explosives

Weight:

approx. 50 kg

Extent of Mechanization:

partly mechanized

Form of Driving Energy.

pneumatic

Mode of Operation:

semi-continuous

Throughput/Capacity:

several 100 kg explosives/hour

ECONOMICAL DATA:

Investment Cost:

not known

Operating Cost:

cost of compressed air and labor

Consequential Cost through Coupling Effects:

cost of supply of compressed air

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Experience:

low |————|————| high

Deposit Requirements:

in coal deposits with methae emission and, in all cases where electric detonation is used, non static hoses have to be applied

Regional Distribution:

wherever prilled explosives are being used

Experience of Operators:

very good |————|————| bad

Environmental Impacts:

low |————|————| very high


mining air pollution by gas and dust blown out by explosives

Suitability for Local Production:

very good |————|————| bad

Under what Conditions:

good metal manufacture with lathe

Lifespan:

very long |————|————| very short

Bibliography, Source: Roschlau

OPERATING PRINCIPLE:

Pneumatic charging machines serve as filling device to insert blasting explosives into the drill hole. Fed by compressed air line or tank, compressed air flows through a venturi Jet. The smaller the cross-section of the Jet is, the higher is the speed of streaming air. In or shortly before the Jet becomes narrowest, granulated explosive is poured into the air stream. The explosive is then transported through a conveying hose into the drill hole.

Another way is to fill a storage tank with explosives and compressed air and discharge at the bottom of the tank. This conveying system is more careful, causes less abrasion and little fine dust particles of the explosive.

In non-mechanized mines, cartridged blasting explosive can be charged with a tamping stick.

AREAS OF APPLICATION:

Charging of prilled explosives in blasting drill holes by using compressed air.

REMARKS:

Charging of drill holes with explosives is being done through the following
steps:

1. Blowing the drill hole clean so that the remaining water caused by drilling flush or influx of crack water is removed. Wet explosive can hardly be fired and occasionally leads to a missed hole. Subsequently, this results to either large size debris or breaking away of the round. To clean the hole, a conveyor hose is placed at the drill bottom to blow compressed air Into the hole which then carries the water out. The control panel should therefore be so designed so as to allow switching of air mix from explosive compressed air to pure air, alternatively.

2. Charging the drill hole with a high explosive blasting cartridge and detonator with electric ignition or ignitor fuse, by using a tamping stick or charging machine. This charging of cartridged explosive serves as the primer detonation. During insertion of the cartridge with detonator, care should be taken that electrical wires are carefully inserted into the bottom of the hole so as not to damage them.

3. Prepared safety explosive (ANC, ANO, ANFO, ANDEX), a mixture of ammonium nitrate (94 %) and oil (6 %) is inserted with the above-mentioned charging machine through the charging hose.

4. Filling of drill holes with clay, small stones or cotters.

Important for a good blasting effect is the correct use of energy which is released during the chemical reaction of explosive. This can be achieved mainly by a complete filling of drill hole with blasting explosive or with explosive components.

SUITABILITY FOR SMALL-SCALE MINING:

Pneumatic charging machines are suitable for local production, very simple and cheap remedies, which allow the use of cheaper ANO explosive.


Fig.: Schematic sketches of the general methods of compressed air charging. Source: Roschlau.


a) Jet stream transport,
b) Transporter with belt betcher,
c) Transporter with porous bottom,
d) Pressure tank transporter.

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